Demand for Radio Frequency Identification (RFID) is increasing rapidly with advancement in integrated circuit (IC) technologies and decreasing size and cost of RFID tags. These enable numerous applications which require very small size and low-cost RFID readers. Some of these applications include tagging items in retail stores, warehouse management, baggage tracing and tracking at the airports. This increase in demand calls for a corresponding need for small form factor and low-cost handheld RFID readers.
RFID frequency bands start from as low as 125 kHz. But for long read range ultra-high frequency (UHF), 860 MHz to 960 MHz band, is preferred since the size of the reader and tags are comparable to wavelength. Further, the 860 MHz to 960 MHz band falls within the approved frequency bands for UHF RFID in major countries. For USA, the minimum frequency resolution is about 50 kHz. EPC Global Class-1 Generation-2 protocol focuses on the frequency band from 860 MHz to 960 MHz. The European RFID standard calls for stringent spectrum mask requirement as disclosed in publication European Telecommunications Standards Institute EN 302 208-1 V1.1.2, European Standard, 2006-03.
There are known single-chip transceivers providing radio frequency (RF), mixed-signal, and digital baseband functionality for a physical layer of a UHF RFID reader. The RFID reader IC has a die size of 21 mm2 and is realized in a 0.18 μm silicon germanium (SiGe) BiCMOS process. The chip dissipates 1.5 W when simultaneously transmitting a +20 dBm signal and receiving −85 dBm tag signals in the presence of a 0 dBm self jammer.
There is also a known complementary metal-oxide-semiconductor (CMOS) RF transceiver for UHF mobile RFID reader operating at 900 MHz band. The transceiver is designed and fabricated in a 0.18 μm CMOS process, where the design focus is on the linearity rather than the noise figure.
There is also a known reader front-end which allows for detection of the tag information in the presence of large in-band blockers, based on the RFID range. The proposed reader allows for amplification of the weakest desired signal by 18 dB while rejecting the TX blocker and its noise floor as well as LO phase noise by 30 dB on average, resulting in a better than 50 dB of signal-to-blocker ratio. TX blocker rejection is achieved through a combination of signals traveling in two RF paths, a linear path and a nonlinear path. In the linear path, both the desired and the blocker signals are equally amplified through a low noise amplifier (LNA) and in the nonlinear path, the desired signal limits both the blocker and the desired signals. The limiting function only preserves the frequency and phase of the stronger blocker signal. The blocker signal is then rejected by subtracting the outputs of the linear and nonlinear paths. Therefore, the blocker signal is cancelled out but the desired signal is amplified through the linear path.
There is a known RFID reader accessible through a personal computer, where the RFID reader includes a PC card interface and a controller both operating according to clock signals from a crystal oscillator. The RFID reader further includes a linearized power amplifier modulator in a transmit path, a receive chain capable of demodulating EPC global Class—1 and Class—0 signals from RFID tags, and an integrated switching device for selecting one of a plurality of antenna for transmitting or receiving RF signals.
Another RFID reader provides sensitivity enhancement for a single antenna RFID interrogating device by separately coupling a nulling signal formed using a portion of a transmit signal into a receiver. The phase and amplitude of nulling signal can be adjusted so that the nulling signal cancels that a reflected transmit signal from the antenna, resulting in the small backscattered signal from the distant RFID tag to be more easily detected, and improving the sensitivity of the RFID receiver.
A known receiver uses a lumped constant network approach to eliminate costly and bulky couplers, circulators and distributed delay lines. A single-pole, four-throw (sp4t) antenna switching arrangement is also provided. The receiver provides a hand-held receiver capable of operation over distances of approximately three to five meters. This allows the construction of a hand-held receiver having high performance (i.e., a long reading distance) and good discrimination (i.e., the ability to accurately read closely-spaced tags moving rapidly past a check point). When used with compatible RFID tags, the system may also be used to alter the identification or other information stored within the RFID tags.
It would be advantageous to have a RFID transceiver that provides the above functions on a single integrated device and yet is able to operate in one of a plurality of predefined frequency ranges. The present invention provides such a RFID transceiver that matches the performance of currently available, but more expensive and bulkier RFID transceivers.